yup!
if you look on "history" you can see when it was edited, and later corrected. here are a few:
"
(correcting date after someone put false date)" --> same day
"
(removing earlier vandalism) (Reverted test and/or vandalism edits by 71.116.138.158)" ----> same day
"(Reverting two vandalism updates)" ----> today, vandalism posted today
So actually, vandalism is corrected very quicky. Wikipedia is definately one of the best, if not the, general resources on the net, IMHO.